simBinTree/oneRunMC.py

# -*- coding: utf-8 -*-
"""
Simulation of a random walk on a finite b-ary tree of depth k

"""

import random as rn
import numpy as np
import matplotlib.pyplot as plt
#import math as mt

rn.seed(0)

k = 10  # depth of the tree
b = 2  # arity of the tree
T = 100  # number of steps taken by the MC

X = np.zeros(T)
Y = np.zeros(T)
Z = np.zeros(T)

for a in range(0, T):
    Z[a] = T

X[0] = rn.randint(0,k)  # setting the starting level for X
Y[0] = rn.randint(0,k)  # setting the starting level for Y

for a in range(0, (T - 1)):
    monX = rn.randint(0,1)
    probArisX = rn.randint(0,(b + 1)) 
    monY = rn.randint(0,1)
    probArisY = rn.randint(0,(b + 1)) 
    if X[a] != Y[a]:  # if X is different to Y
        if X[a] > 0 and X[a] < k:  # if the MC is in the middle depths of the tree
            if monX == 1: 
                X[a + 1] = X[a]
            if monX == 0: 
                if probArisX == 0:
                    X[a + 1] = (X[a] - 1)
                if probArisX != 0:
                    X[a + 1] = (X[a] + 1)
        if X[a] == 0:  # if the MC is in the root node
            if monX == 1: 
                X[a + 1] = X[a]
            if monX == 0:
                X[a + 1] = (X[a] + 1)
        if X[a] == k:  # if the MC is in the leaf of the tree
            if monX == 1: 
                X[a + 1] = X[a]
            if monX == 0:
                X[a + 1] = (X[a] - 1)
        if Y[a] > 0 and Y[a] < k:  
            if monY == 1: 
                Y[a + 1] = Y[a]
            if monY == 0: 
                if probArisY == 0:
                    Y[a + 1] = (Y[a] - 1)
                if probArisY != 0:
                    Y[a + 1] = (Y[a] + 1)
        if Y[a] == 0:
            if monY == 1: 
                Y[a + 1] = Y[a]
            if monY == 0:
                Y[a + 1] = (Y[a] + 1)
        if Y[a] == k:
            if monY == 1: 
                Y[a + 1] = Y[a]
            if monY == 0:
                Y[a + 1] = (Y[a] - 1)
    
    if X[a] == Y[a]:  # if X is equal to Y
        Z[a] = a
        if X[a] > 0 and X[a] < k:
            if monX == 1: 
                X[a + 1] = X[a]
                Y[a + 1] = X[a]  #X[a + 1]
            if monX == 0: 
                if probArisX == 0:
                    X[a + 1] = (X[a] - 1)
                    Y[a + 1] = (X[a] - 1)  #X[a + 1]
                if probArisX != 0:
                    X[a + 1] = (X[a] + 1)
                    Y[a + 1] = (X[a] + 1)  #X[a + 1]
        if X[a] == 0:
            if monX == 1: 
                X[a + 1] = X[a]
                Y[a + 1] = X[a]  #X[a + 1]
            if monX == 0:
                X[a + 1] = (X[a] + 1)
                Y[a + 1] = (X[a] + 1)  #X[a + 1]
                    
        if X[a] == k:
            if monX == 1: 
                X[a + 1] = X[a]
                Y[a + 1] = X[a]  #X[a + 1]
            if monX != 1:
                X[a + 1] = (X[a] - 1)
                Y[a + 1] = (X[a] - 1)  #X[a + 1]
                    
                      
#plt.plot(X,'ro',ms=0.8)
#plt.plot(Y,'bo',ms=0.8)
plt.plot(X,'r')
plt.plot(Y,'b')
plt.show()                
                
t = np.amin(Z)                  
print("t_cou = " + str(t))

#n = (mt.pow(b,k + 1) - 1)/(b - 1)  # number of vertex in the tree T_{b,k}  b - arity, k - depth

#if t != 0:
#    if t <= ((4 * n)/T):
#        print("The test is passed")
#else:
#    print("The MC started coupled")